Experiments on Struts Piercing the Water Surface

Abstract

Water tunnel measurements were made on rectangular bar and circular cylinder struts piercing the free water surface. These were run at several depths and velocities in order to measure drag forces and to investigate the mechanism by which air often ventilates down behind such struts. It was found that the ventilation mechanism depends on viscous wake phenomena in a manner similar to ventilation behind fully-submerged bodies. Moreover, in fully-ventilated flow the forces are well predicted by application of two-dimensional cavity theory. A hysteresis effect on ventilation and forces was observed and found to be caused by surface tension. This last may explain some discrepancies between the present drag data and that previously taken on circular cylinders in a towing tank.

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